The present invention generally relates to heat exchange apparatus employing tubes which contain fluid flow within a heat exchange system. More particularly, the invention pertains to heat exchange tubes used in such apparatus and having internal projections or turbulating structure for promoting more efficient heat transfer by the apparatus.
Heat exchange tubes are used to transfer heat between two media by utilizing, for example, a so-called "tube-in-tube" design or a "shell-in-tube" design. In a "tube-in-tube" design the fluid product to be heated or cooled flows through a product tube or series of product tubes and the heating or cooling media flows through an outer media tube or series of media tubes usually in a countercurrent fashion with respect to the product flow. Thus, heat is transferred between the media flowing in the inner space between the walls of the media and product tubes and the fluid product flowing through the product tubes or tubes. In a "shell-in tube" design the product tubes are disposed within a container referred to as a shell and within which the heating or cooling media flows over all of the product tubes from an inlet to an outlet thereof to transfer heat between the media and the product.
To improve heat transfer efficiency the product tubes in either a tube-in-tube design or shell-in-tube design have included turbulating structure of various configurations to promote turbulent flow within the tube. Generally stated, turbulent flow increases the heat transfer efficiency of the tube by distributing the fluid flowing therethrough across the entire diameter of the tube and not in streams flowing generally parallel to the axis of the tube. Since a higher rate of heat transfer occurs adjacent the wall of the product tube, ideally a flow pattern is created which eliminates a temperature gradient within the fluid at any cross section taken through the tube. Various types of turbulating structure have been disclosed, for example, in U.S. Pat. Nos. 2,343,542; 4,314,587; 4,330,036; 4,425,942; 4,470,452; 4,794,983; and 4,880,054.
A problem which exists in all of the known prior art is that of obtaining a maximum amount of turbulence within a heat exchange tube while still allowing fast, complete drainage of the tube at the end of a heating or cooling process. This is especially critical in the food processing industry where product tubes which contain, for example, fluid food product such as juice must be drained and sterilized after use to prevent the growth of bacteria. Fast, complete drainage of the product tubes is therefore necessary to inhibit bacterial contamination of the processing equipment and subsequent contamination of fluid food product. Prior heat exchange tubes with turbulating structure have included such structure on an inner bottom surface of the tube such that even when the tube is drained, some product is prevented from exiting the tube by the turbulating structure. In the food industry this product is left in the tube to promote harmful bacteria growth. Other heat exchange tubes have failed to provide turbulating structure which both maximizes heat transfer efficiency and allows fast, complete drainage of the tube.